Many different types of printing have been invented, a large number of which are presently in use. The known forms of print have a variety of methods for marking the print media with a relevant marking media. Commonly used forms of printing include offset printing, laser printing and copying devices, dot matrix type impact printers, thermal paper printers, film recorders, thermal wax printers, dye sublimation printers and ink jet printers both of the drop on demand and continuous flow type. Each type of printer has its own advantages and problems when considering cost, speed, quality, reliability, simplicity of construction and operation etc.
In recent years, the field of ink jet printing, wherein each individual pixel of ink is derived from one or more ink nozzles has become increasingly popular primarily due to its inexpensive and versatile nature.
Many different techniques on ink jet printing have been invented. For a survey of the field, reference is made to an article by J Moore, “Non-Impact Printing: Introduction and Historical Perspective”, Output Hard Copy Devices, Editors R Dubeck and S Sherr, pages 207-220 (1988).
Ink Jet printers themselves come in many different types. The utilization of a continuous stream of ink in ink jet printing appears to date back to at least 1929 wherein U.S. Pat. No. 1,941,001 by Hansell discloses a simple form of continuous stream electro-static ink jet printing.
U.S. Pat. No. 3,596,275 by Sweet also discloses a process of a continuous ink jet printing including the step wherein the ink jet stream is modulated by a high frequency electro-static field so as to cause drop separation. This technique is still utilized by several manufacturers including Elmjet and Scitex (see also U.S. Pat. No. 3,373,437 by Sweet et al)
Piezoelectric ink jet printers are also one form of commonly utilized ink jet printing device. Piezoelectric systems are disclosed by Kyser et. al. in U.S. Pat. No. 3,946,398 (1970) which utilizes a diaphragm mode of operation, by Zolten in U.S. Pat. No. 3,683,212 (1970) which discloses a squeeze mode of operation of a piezoelectric crystal, Stemme in U.S. Pat. No. 3,747,120 (1972) discloses a bend mode of piezoelectric operation, Howkins in U.S. Pat. No. 4,459,601 discloses a piezoelectric push mode actuation of the ink jet stream and Fischbeck in U.S. Pat. No. 4,584,590 which discloses a shear mode type of piezoelectric transducer element.
Recently, thermal ink jet printing has become an extremely popular form of ink jet printing. The ink jet printing techniques include those disclosed by Endo et al in GB 2,007,162 (1979) and Vaught et al in U.S. Pat. No. 4,490,728. Both the aforementioned references disclosed ink jet printing techniques that rely upon the activation of an electrothermal actuator which results in the creation of a bubble in a constricted space, such as a nozzle, which thereby causes the ejection of ink from an aperture connected to the confined space onto a relevant print media. Printing devices utilizing the electro-thermal actuator are manufactured by manufacturers such as Canon and Hewlett Packard.
As can be seen from the foregoing, many different types of printing technologies are available. Ideally, a printing technology should have a number of desirable attributes. These include inexpensive construction and operation, high speed operation, safe and continuous long term operation etc. Each technology may have its own advantages and disadvantages in the areas of cost, speed, quality, reliability, power usage, simplicity of construction operation, durability and consumables.
The present Applicant has described a plethora of inkjet printheads, which are constructed utilizing micro-electromechanical systems (MEMS) techniques. As described in the Applicant's earlier U.S. application Ser. Nos. 11/685,084; 11/763,443; and 11/763,440, the contents of which are incorporated herein by reference, a MEMS inkjet printhead may comprise a nozzle plate having moving portions. Each moving portion typically has a nozzle opening defined therein so that actuation of the moving portion results in ejection of ink from the printhead.
An advantage of this type of printhead is that the energy required to eject a droplet of ink is small compared with, for example, traditional thermal bubble-forming printheads. The Applicant has previously described how specific actuator designs and complementary actuation methods provide highly efficient drop ejection from such printheads (see, for example, U.S. application Ser. Nos. 11/607,976 and 12/239,814, the contents of which are herein incorporated by reference).
However, a problem with ‘moving nozzle’ printheads is that they require a good fluidic seal between the moving portion and the stationary portion of the printhead. Ink should only be ejected through the nozzle opening and should not leak out of seals. If the distance between the moving portion and the stationary portion is small, then surface tension may retain ink inside nozzle chambers. However, the use of ink surface tension as a fluidic seal is problematic and usually cannot provide a reliable seal, especially if the ink inside nozzle chambers experiences pressure surges.
In the Applicant's earlier application Ser. Nos. 11/685,084; 11/763,443; and 11/763,440, there was described a method of fabricating a mechanical seal for moving portions of a nozzle plate. Typically, a flexible layer of polydimethylsiloxane (PDMS) is coated over the nozzle plate, which acts as a sealing membrane between the moving portions and the stationary part of the printhead. Moreover, the layer of PDMS provides a hydrophobic ink ejection surface, which is also highly desirable in terms of printhead fluidics and, ultimately, print quality.
It would be desirable to provide improved mechanical seals for inkjet printheads having moving nozzles. It would be particularly desirable to provide efficacious mechanical seals, which have minimal impact on the overall efficiency of the printhead.